Overview
ISO 13909-8:2025 - Coal and coke - Mechanical sampling - Part 8: Methods of testing for bias describes principles and procedures for testing the bias of test samples of coal and coke collected according to the ISO 13909 series. The third edition (2025) updates reference method requirements and aligns titles within the series. The standard explains how to design and conduct field bias tests, how to collect paired samples (system under test vs. reference), and how to apply statistical analysis to determine sampling bias.
Key topics and technical requirements
- Purpose: Establish procedures to detect bias introduced by mechanical sampling systems or components.
- Reference method: The preferred reference is the stopped-belt method - collecting increments from a full cross-section of material on a stopped conveyor using a sampling frame. Stopped-belt increments should be taken for a belt length at least three times the nominal top size of the fuel.
- Pretest inspection: Thorough static and dynamic examination of the sampling system and component specifications, following guidance in ISO 21398. Fix known bias sources before testing unless deliberately assessing a system “as is.”
- Test design elements:
- Choice of parameters: Standard tests should include moisture and ash (on a dry basis); additional variables are optional but may reduce test sensitivity.
- Number of paired samples: Minimum 30 paired samples; more may be needed if fuel variability is high.
- Selection of sample pairs: Guidance for paired-increment and paired-batch sampling, and considerations specific to coke (size-distribution tests often needed).
- Sample handling: Collect, prepare, and document samples carefully; determine increment/sample mass immediately and report any losses.
- Statistical analysis: Tests assume multivariate normality, independence of measurement errors, and homogeneity. Procedures include outlier identification, confidence-interval calculations, and interpretation of bias (see Annex A for example calculations).
Practical applications
- Verifying that conveyor and mechanical sampling systems produce unbiased representative samples for quality control, contract verification, regulatory compliance, and laboratory testing.
- Assessing system components (e.g., samplers, crushers, diverters) and identifying sources of moisture or size-distribution bias.
- Supporting commissioning, periodic audit testing, or dispute resolution between suppliers and buyers.
Who should use this standard
- Sampling engineers and technicians, QA/QC and laboratory managers, mine and port operators, industry auditors, equipment manufacturers, and consultants involved in bulk solid fuel sampling and analysis.
Related standards
Keywords: ISO 13909-8:2025, mechanical sampling, coal sampling bias, coke sampling bias, stopped-belt method, sampling frame, paired samples, moisture and ash testing, sampling system validation.
